In a process of fabricating a semiconductor device, by using so-called photolithography technique, a predetermined circuit pattern is formed on the surface of a semiconductor wafer. In the photolithography process, for example, a series of processes of applying a photoresist solution on a semiconductor wafer subjected to a cleaning process to thereby form a resist film, exposing the resist film in a predetermined pattern, and developing the exposed resist film are performed.
A resist film is formed by, for example, the following process. First, a semiconductor wafer is fixed to a spin chuck. Next, for example, by using a resist solution discharge nozzle having, at its end, a tube member in which the diameter of a path of the resist solution is constant, a predetermined amount of the resist solution is applied to the surface of the wafer. By rotating the spin chuck in such a state, the resist solution is spread to the entire wafer and the thickness is adjusted to a predetermined thickness. After that, the wafer is subjected to predetermined heat treatment, to be specific, a pre-baking process.
Conventionally, the resist film pre-baking process is performed by using a heating unit 101 shown in FIG. 10. Heating unit 101 has a chamber 102, a hot plate 103 provided in chamber 102, an air inlet 104 for introducing a predetermined amount of air into chamber 102, and an exhaust port 105 for exhausting a predetermined amount of air in chamber 102. In such heating unit 101, a wafer is placed on hot plate 103 held at a predetermined temperature and is heated. Concurrently with the operation, while introducing a predetermined amount of air into chamber 102 from air inlet 104 and exhausting the same amount of air from exhaust port 105, a resist film pre-baking process is performed.
In recent years, in the photolithography process, as a pattern is becoming finer and thinner, uniformity in a wafer plane of pattern line width (hereinafter, referred to as “CD (Critical Dimension) uniformity”) is strictly demanded. A resist material started to appear in which line width fluctuations occur conspicuously due to air current in the heating unit for performing a pre-baking process after application of a resist, that has not been a problem. However, in a conventional heat treatment method performed by using heating unit 101 while allowing air to flow in chamber 102, since it is considered that variations occur in density of polymer included in the resist solution or density of residual solvent due to a change in the surface temperature of the resist film caused by air current, the conventional technique cannot deal with such a problem.
As a pattern is becoming finer and thinner, it is becoming more important to control roughness of a side face of a pattern (hereinafter, referred to as “LER (Line Edge Roughness”). As a method of solving the problem of LER, adjustment of compositions of the resist solution is being attempted. However, a sufficient effect has not been produced in relation to other resist characteristics such as resist sensitivity and CD uniformity. On the other hand, there is no approach from the heating unit side to LER.